The present invention relates to implementing direct data access from a digital mobile network to data networks, such as packet networks or local area networks (LAN).
Mobile systems have been developed due to the need to enable people to move away from desktop telephone sets and to reach people even when they are outside a certain location. As automation becomes a permanent part of the working environment, people outside offices feel the need to use a computer anywhere and to be able to connect from any place to any place. Therefore it seems inevitable that mobile systems providing speech services develop towards data services.
Computer technology makes it possible to produce light-weight portable equipment with a better processing capacity, storage capacity and user friendliness. This development of computers has made it technically possible and economically reasonable to provide mobile data services. In such cases the user has mostly likely a mobile telephone for speech traffic, wherefore the best way to provide data transmission is to perform it via the mobile system to great extent in the same way as data transmission via a conventional telephone network.
The introduction of digital mobile systems, such as the Pan-European mobile system GSM, signifies a breakthrough in supporting mobile data transmission in general-purpose cellular networks. Since the GSM is an entirely digital system and operates according to the general principles of the ISDN (Integrated Services Data Network), the GSM is naturally capable of transferring data. As regards the type of the data network, the GSM does not represent a dedicated transmission network but an access network. In other words, the purpose of data transmission via the GSM is to provide access to the actual data networks.
The GSM network provides a great number of services to the subscribers. In addition to speech and emergency call services, the GSM network supports all types of low-rate data transmission services that the present data transmission offers. The only limitation results from the capacity of the radio interface that restricts the data rate to 9.6 kbit/s.
Therefore a modern digital mobile system, such as the GSM, can be used for connecting any data terminal, such as a remote-work station, to a computer or a desired data network, such as a LAN. FIG. 1 illustrates different known methods of realizing such a data link. A terminal equipment TE generally consists of a conventional work station (e.g. a portable PC) that is connected to the data interface of the mobile station MS. The mobile network (PLM) typically requires, both in the terminal equipment interface (MS) and in the network interface (mobile switching centre MSC), a special adapter for adapting an internal data link of the PLMN to the terminal equipments and/or to other data links/transmission systems, such as the PSTN, LAN or PSDN. The adapter connected to the MS is generally called a terminal adapting function (TAF) and the adapter provided at the network end is called an interworking function (IWF). In the GSM mobile network such an interworking function is typically situated in connection with the MSC.
In such a network configuration, the TE may have a data communication via the radio path with an IWF placed in connection with the MSC, and thereby with a host computer CPU connected to another transmission network. The IWF may comprise for example a data modem MOD1 that sets up a modem connection via the public switched telephone network PSTN to another data modem MOD2 or MOD3. The other data modem may be connected directly to the terminal equipment or to the computer CPU in the same way as modem MOD2. However, this other modem is often connected to a LAN server connected to the LAN, the server being used to establish a remote connection to the LAN. Via the LAN it is in turn possible to establish a connection for example to a desired computer HOST. The problem of the PSTN modem connection is, however, the generally low transfer rate and poor bit error ratio. In such a case, the bit rate and the bit error ratio of the entire data connection are also in accordance with the PSTN and therefore of clearly lower quality than what the GSM network can offer, for example.
The solution to this problem is a direct data access from the MSC to the data network. In such a case, the IWF provides an interface to which it is possible to connect the external devices, which in turn provide a gateway to the current data network. Such external devices include for example LAN servers that operate as a gateway to LANs, and PAD devices that operate as a gateway to packet networks. A PAD device (Packet Assembly/Disassembly) converts the asynchronous characters (that are used in the PLMN) into data packets (employed in the packet network) and vice versa. These external devices that do not belong to the MSC hardware but to the networks are denoted in the present application with the common name DDA (Direct Data Access) devices.
In digital mobile networks, the functions of the IWF generally also include various rate adaptations and error correcting transmission protocols that must always be carried out by the MSC in the area of which the MS is currently located. For example in the GSM system rate adaptations (RA) and a radio link protocol (RLP) are defined. The RLP is a data transmission protocol wherein error cancellation is based on the retransmission of deteriorated frames after a request from the receiving party. The RLP spans from the TAF of the MS to the IWF. The RA and RLP adaptations of each call must be carried out in the MSC currently serving the mobile station. Therefore each MSC in the present mobile networks must have a connection to each DDA device and from there to each data network. This is not a problem when the data networks are large in size and their number is small. Problems occur when private local area networks or packet networks of companies are to be connected to a mobile network. Assume for example that a company LAN is situated physically within the area of one MSC 1 (for example in Tampere in Finland) and it can easily be provided with a DDA. If however the company personnel roams also within other MSC areas (for example in Helsinki), the DDA to the company LAN must be implemented separately in each MSC. This has proved to be very difficult and expensive both for the network operators and the client companies. This arrangement further fails to allow the use of a direct data access when the mobile subscribers are roaming in another mobile network, for example in Sweden.
The object of the present invention is to provide a direct data access from a mobile network to data networks in such a way that it would not be necessary to introduce the data access of each data network separately to each of the switching centres in the mobile network, but there is a centralized data access in one of the network. switching centres.
This is achieved with an arrangement for providing a direct data access from a digital mobile network to a data network, such as a packet network or a local area network. The arrangement is characterized according to the invention by
a direct data access to a data network implemented in a centralized manner in a first switching centre of the mobile network,
a directory number allocated to the direct data access,
a second switching centre arranged to route a data call, made from a mobile station situated within the service area of the second switching centre to said directory number, to said first centre as a digital data call according to a bearer service supported by the mobile network,
interworking functions for said routed data call being divided between the first and the second switching centre in such a way that said first switching centre comprises a first interworking function that provides the adaptation functions required by said centralized data access and said digital bearer service, and said second switching centre comprises a second interworking function that provides the adaptation functions required by a data link established over the radio path and the adaptation functions required by said digital bearer service.
In the invention, the adaptation functions of a conventional network termination that implements a direct data access to a data network are divided into two parts: 1) the normal adaptation functions of a mobile network, such as rate adaptation or transmission protocol, and 2) adaptation functions that provide a data access for a DDA device of a data network. The former functions are placed in the serving switching centre of the mobile station. The latter functions are placed in the switching centre provided with the centralized DDA to the data network. The connection between these two functions employs a bearer service of the mobile network supported by at least a majority of the mobile switching centres. In the preferred embodiment of the invention, this bearer service is unrestricted digital information (UDI) which is defined in most digital mobile networks for ISDN connections. In practice the UDI bearer service is applied in such a way that a data call is routed as a UDI call from the serving switching centre to the switching centre provided with the centralized DDA. The invention has the advantage that the first adaptation function according to the invention and the associated routing of the data call can be realized at any switching centre, i.e. a switching centre of any manufacturer or a switching centre located in any network supporting the UDI bearer service or any other selected bearer service. The DDA adaptation functions provided in the other switching centre will adapt the UDI data call to the DDA device of each data network. Thus, one centralized DDA in one mobile switching centre can provide access to a data network from any other switching centre supporting the UDI bearer service.
From the serving switching centre point of view, the data call according to the invention is a normal asynchronous data call using the UDI bearer service. The call is routed to the other (target) switching centre on the basis of a dialled directory number. If the signalling between the serving MSC and the target MSC supports the transmission of bearer capability information, the traffic channel parameters arriving from the MS in the format employed in the mobile network are forwarded to the IWF of the target MSC. If there is no signalling support available to the bearer capability information, the target MSC uses the default profile (user rate, character structure) according to the dialled directory number, in order to set up a traffic channel for the data access. Also in this case there may be several profiles for the data access, and each profile being assigned has a dedicated directory number. Another alternative in a situation where the call set-up signalling from the servicing MSC does not contain the bearer capability information is that the target MSC requests for this information from the serving MSC.
Since the UDI used in the invention is a bearer service also supported by the ISDN, the data calls according to the invention to a direct data access are not restricted to the mobile network. A data call may also originate from the ISDN or PSTN.
If an MSC comprising a centralized DDA is itself the serving MSC, both adaptation functions are performed in the same MSC, as in conventional systems.